1. Field of the Invention
This invention relates to the techniques for improving the productivity of semiconductor devices, and more particularly to the techniques for preventing the electrostatic destruction of switching elements, such as thin film transistors (TFT""s).
The semiconductor devices referred to in this specification indicate all of devices capable of being operated by utilizing the characteristics of a semiconductor, and an electro-optic device (which will hereinafter be referred to as a display), a semiconductor circuit and electronic equipment are all semiconductor devices.
2. Description of the Related Art
In recent years, the techniques for forming a TFT by using a semiconductor film (of around several to several hundred nm in thickness) provided on an insulating surface-carrying substrate have attracted the technicians"" attention. A TFT is applied extensively to electronic devices, such as an integrated circuit (IC) and an electro-optic apparatus, and the development of the TFT as a switching element, especially, a liquid crystal display and a luminescent apparatus (EL type display) has been hastened. The switching element referred to in this specification indicates an element capable of attaining two modes of condition, i.e. an ON condition in which the resistance is low due to a voltage applied from the outside, and an OFF condition in which the resistance is high. and carrying out switching operations in accordance with the ON and OFF actions.
Accordingly, the use of a recent liquid crystal display as a monitor and a display of a portable terminal device is increasing, and the mass production of such liquid crystal displays is being forwarded.
In the manufacturing of an ultra-large-scale integrated circuit (ULSI), the manufacturing environment constitutes one of the factors having a large influence upon the yield and reliability of the product. There are many factors to be controlled and eliminated which include temperature and humidity, microvibration, static electricity, magnetic field variation and impurities. Therefore, the improvement of the yield and reliability of the products depends upon the way of attaining a high-quality environment. Regarding the providing of a high-quality environment, the occurrence of static electricity constitutes a factor exerting the greatest influence upon the improvement of the yield and reliability of the products.
Therefore, how to prevent the occurrence of static electricity comes to be important in a step of assembling such displays as mentioned above. In this specification, a liquid crystal display will be described as an example of a semiconductor device. A procedure for assembling a related art liquid crystal display will be described briefly with reference to FIG. 6.
(1) An element substrate is manufactured. The element substrate will hereinafter be referred to as an active matrix substrate.
(2) Spacers corresponding to desired cell gaps are provided, and a space between the active matrix substrate 601 and a counter-substrate 602 is thereby retained. The active matrix substrate 601 and counter-substrate 602 are bonded together with a sealant 609.
(3) The active substrate 601 and counter substrate 602 are pasted on each other, and the resultant product is thermally pressed. The thermal pressing is a step for manufacturing a panel not having an uneven space between the active substrate 601 and counter-substrate 602 by curing the thermosetting sealant with heat, and further applying pressure to the resultant product.
(4) A pair of pasted and thermally pressed substrates are divided into parts of a predetermined shape. The cutting is done so that a short-circuiting ring 606 (a portion shown by a thick line in FIG. 6) is left on a terminal end (end portion) of a wiring portion 605.
(5) The injecting of liquid crystals is done, and an injection port is sealed.
(6) The panel is washed.
(7) A re-orientation operation is carried out.
(8) The short-circuiting ring 606 is removed by chamfering, and the chamfered portion is washed.
(9) The fixing of a flexible printed circuit (FPC) is done. The flexible printed circuit will hereinafter be referred to as FPC.
The pasting of a polarizing plate is then carried out.
Since the active matrix substrate 601 is handled by an insulating material rarely contaminated with a metal and having a chemical resistance, the charge potential of the active matrix substrate 601 is high. A glass substrate itself mainly used for the active matrix substrate 601 and counter-substrate 602 is an insulator. Therefore, even when these substrates are handled by a conductive material, it is difficult to prevent the substrates from being electrically charged. When static electricity occurs in the insulating substrates, it causes switching elements and a holding capacitor (add-on capacitor) formed on the active matrix substrate 601 to be destroyed, and the characteristics of a TFT to be deteriorated, so that the quality of an image becomes low.
The short-circuiting ring 606 is provided so as to prevent the electrostatic destruction (destruction by static electricity) of a display picture element portion 603 on the active matrix substrate 601, and switching elements provided in peripheral driving circuits 604 thereon. The short-circuiting ring represents a wiring pattern for short-circuiting the terminal ends of wires on the active matrix substrate so as to prevent the electrostatic destruction of the switching elements. Namely, the short-circuiting ring is formed mainly of the portion of the conductor which is provided in parallel with an end surface of the active matrix substrate. The short-circuiting ring may not have an annular shape. It is usually necessary that the short-circuiting ring be removed before a point in time at which the manufacturing of the display is completed with the displaying of an image started. In the above-described display assembling procedure, the short-circuiting ring 606 is removed in the chamfering step, a final step of the panel assembling operation.
When the manufacturing of a liquid crystal display is done by such a related art liquid crystal display assembling procedure, the short-circuiting ring 606 (portion shown by a thick line in FIG. 6) is removed in the chamfering step (8). Therefore, the electrostatic destruction of the switching elements occurs in some cases in the operations in the chamfering step (8) to the FPC fixing step (9), and, in such cases, a decrease in the yield occurs.
The causes of the occurrence of the static electricity are classified into two, i.e. frictional charge occurring in a contact-separation operation, and charge occurring due to the supply of electric charge from the outside. In the chamfering step (8) above, frictional charge occurs due to the contact and separation of a chamfering unit with and from an end surface of a substrate. In the FPC fixing step (9), frictional charge occurs due to the contact of FPC with the wiring portion. Since the FPC fixing step (9) relies partially upon a handling operation, electric charge due to the supply of electric charge from the outside necessarily occurs. Due to the various types of electric charge mentioned above, electric discharge occurs via the thin insulating film provided on the TFT to cause the insulating characteristics of the TFT to be lost, and troubles to occur in a control unit which handles minute electric signals. Although the occurrence of static electricity is prevented in the chamfered portion washing step following the chamfering step, the electrostatic destruction of switching elements occurs with a probability of 9.1% in the operations in the chamfering step (8) to the FPC fixing step (9). Therefore, it is necessary that the electrostatic destruction of such elements be prevented in these steps.
The present invention has been made in view of the above-mentioned circumstances, and provides concerning a display dividing method, the techniques for obtaining a liquid crystal display capable of reducing the electrostatic destruction of switching elements and having a high yield.
According to the present invention, the electrostatic destruction of switching elements occurring due to the operations in the chamfering step to the FPC fixing step can be reduced by removing an electrostatic destruction preventing short-circuiting ring from an upper surface of an active matrix substrate by a substrate dividing operation after a short-circuiting bar-carrying FPC is fixed.
Since the short-circuiting ring has a function of preventing the electrostatic destruction of switching elements, it is desirable that the removing of the short-circuiting ring be done after the execution of the FPC fixing step. After the wiring portion on the side of the display and FPC are connected together, the detachable short-circuiting bar provided on the side of the FPC works also as a short-circuiting ring. Therefore, even when the short-circuiting ring is removed, a problem does not occur. The short-circuiting bar referred to in this specification is a conductor provided on the FPC. Even when the short-circuiting bar-carrying FPC and wiring portion on the active matrix substrate are connected together, the wiring portion on the active matrix substrate (including the wiring portion provided on the peripheral driving circuits and display picture element portion) can maintain their short-circuited condition even though the short-circuiting ring is cut off from an upper portion of the active matrix substrate.
According to an aspect of the present invention, the method of manufacturing semiconductor devices has the steps of:
preparing an active matrix substrate having a conductor formed of a wiring portion and a short-circuiting ring,
connecting a short-circuiting bar-carrying flexible printed circuit to the wiring portion, and
thereafter cutting off the short-circuiting ring from the conductor.
According to another aspect of the present invention, the method of manufacturing semiconductor devices has the steps of:
preparing an active matrix substrate having a conductor formed of a wiring portion and a short-circuiting ring, connecting a short-circuiting bar-carrying flexible printed circuit to the wiring portion, and
cutting of f the short-circuiting ring from the conductor simultaneously with the circuit connecting operation.
According to still another aspect of the present invention, the method of manufacturing semiconductor devices is in accordance with the first- or second-mentioned method, in which the short-circuiting ring is cut off from the conductor by dividing the active matrix substrate.
According to a further aspect of the present invention, the method of manufacturing semiconductor devices is in accordance with the third-mentioned invention, in which the substrate dividing operation is carried out by using a scriber and a breaking machine.
According to another aspect of the present invention, the method of manufacturing semiconductor devices is in accordance with the third-mentioned invention, in which the substrate dividing operation is carried out by using a dicer.
According to still another aspect of the present invention, the method of manufacturing semiconductor devices is in accordance with the third-mentioned invention, in which the substrate dividing operation is carried out with a laser cutter.